In a conventional valve gear device such as that disclosed in U.S. Pat. No. 4,770,137 issued on Sep. 13, 1988, an intake and exhaust valve is secured to a stem which is movably supported in an engine block. A body is fitted in the block and a top end of the body is in engagement with a rotating cam so that the body is reciprocally movable in the vertical direction. In the body, a plunger is fitted so as to be movable in the horizontal direction. When a top end of the stem which is continually biased by a spring is in engagement with a plunger which is at its first position, the reciprocal movement of the body together with the plunger is established, thereby establishing reciprocal movement of each of the stem and the intake and exhaust valve. Thus, in accordance with the rotation of the cam, the intake and exhaust valve performs opening and closing operations.
In the foregoing structure, if a continual closed condition of the intake and exhaust valve is desired, the plunger is moved to its second position. Then, the stem is brought into disengagement with the plunger and is moved into the body by a biasing force of the spring so that the stem is not affected by the movement of each of the body and the plunger.
However, whenever the plunger moves, the plunger is in sliding engagement with the top end of the stem. As a result, frictional wear of the stop end of the stem is inevitable. Thus, with the passage of time, the lift quantity of the intake and exhaust valve unexpectedly and undesirably varies.